Railway car trucks generally comprise a pair of wheel sets mounted on laterally spaced side frames. The side frames are mounted on the underside of a railway car by means of a bolster. The bolster extends transversely of the car and the opposite ends thereof extend through openings in the side frames. The bolster ends are resiliently supported in the side frames for limited vertical snubbed movement. Such snubbed movement is achieved by a resiliently supported friction shoe disposed between friction surfaces on the bolster and side frame.
To reduce wear of the truck structure and to improve the riding characteristics thereof it is desirable that the trucks be constructed to minimize or eliminate "rocking" and "lozenging". "Rocking" as used herein defines the tendency of the bolster to turn about its lengthwise axis relative to the side frames as occurs for example during humping. "Lozenging" as used herein is the tendency of the spaced side frames to turn about a vertical axis at the bolster ends so that the wheel sets and the side frames form in the nature of a parallelogram rather than remaining in substantially square or tram relationship.
U.S. Pat. Nos. 3,109,387 and 3,408,955 are illustrative of structures which have been used to minimize such lozenging and rotation. Generally both of the patent structures employ flat complementary surfaces formed on the bolster and side frames which are of sufficient length and width to maintain the lozenging and rotation to a minimum. The flat surfaces commonly designated as lands have been arranged in parallel relationship to the friction surface mounted on the side frame.
While the structure of the truck including the lands formed thereon are operative and effective to minimize the lozenging and rotation, there is still a limited amount of permissible relative turning of the bolster ends and side frame. During such "permissible turning" the upright edges of lands tend to gouge its complementary land so as to cause fatigue failure thereof. This failure of the land or stop surfaces requires repair of the surfaces as by welding or the like.